The recent increasing use of heat recuperation for energy conservation purposes has resulted in an increasing number of systems in which the air supplied to the burner has been preheated by a heat recuperator. In the prior art, controls for such systems generally operated off the ambient air line, that is to say, the prerecuperator air line. Two problems can occur with such controls. First, they do not compensate for variations that may occur in the temperature of the air exiting the recuperator. Second, they do not allow for leaks that may occur within the recuperator where air may leak directly into the exhaust line without flowing into the burner.
An improved apparatus for compensating for the temperature of the combustion air supplied to a burner is disclosed in U.S.S.N. 556,766, filed Dec. 1, 1983, and assigned to the assignee of the instant invention, and the teachings of this application are hereby incorporated by reference.
A compensator in accordance with the above-described application comprised a housing having an opening for bleeding air therethrough. There is a tapered plug in the opening which is fastened to a thermostatic metal within the housing. The cross sectional area of the plug is less than the area of the opening, the clearance around the plug being a free flow area through which air bleeds out of the compensator. The thermostatic metal is heated by the air entering the compensator. When the temperature of the air increases, the thermostatic metal is heated and deflected, thereby displacing the plug within the opening and increasing the free flow area. As a result, more air is bled out of the compensator, thereby increasing the pressure drop across the compensator.
While the compensator employing the thermostatic metal performs well, there is a lapse in operating time because of the inclusion of the thermostatic metal within the compensator housing. Also, because the compensator was located in the side wall of the recuperator housing, the compensator housing and the ceramic wall of the recuperator acted as heat sinks and caused a lag in temperature response. The design is also difficult to machine and expensive to install.
It is, therefore, an object of this invention to obviate the disadvantages of the prior art.
It is another object of the invention to enhance temperature compensators.
It is a further object of the invention to enhance recuperator operation.
These objects are accomplished, in one aspect of the invention, by the provision of a multi-pass ceramic recuperator assembly which comprises a recuperator body having a first set of passages for receiving and passing an exhaust gas and a second set of passages, orthogonal to the first set, for receiving and passing a combustion gas.
A housing is provided for the body, and has oppositely disposed inlet and outlet means for the combustion gas communicating with the second set of passages. The inlet and outlet means include baffles which divide the second set of passages into a serpentine path which includes an entrance segment, an intermediate segment, and an exit segment.
A temperature compensator is mounted within the gaseous flow of the intermediate segment. The compensator employs a thermostatic bi-metal which is mounted on the outside of the compensator housing.
Devices constructed as above remove the objectionable features of the prior art. Mounting the bi-metal on the exterior of the compensator housing, directly in the gaseous flow, increases the response time. Also, mounting the compensator in the intermediate flow segment grants greater control since the bi-metal is exposed to lower temperatures.